Glaucoma is the second leading cause of blindness worldwide and results in the degeneration of retinal ganglion cell axons and retinal ganglion cell (RGC) death. Strong evidence supports the idea that RGC axons are initially damaged due to structural alterations in the lamina cribrosa within the optic nerve head (ONH). However, the vast majority of supporting studies are based on data from excised eyes. A lack of high- resolution in vivo imaging data of the normal and glaucomatous lamina cribrosa has prevented thorough understanding of the impact of changes in laminar geometry on disease progression in the living eye. This proposed work will test the hypothesis that structural alterations in laminar pores underlie subsequent axonal damage and vision loss in the normal aged eye and eyes with glaucoma. The hypothesis will be examined by pursuing three specific aims. The first aim will measure in vivo changes in laminar pore geometry over the time course of experimental glaucoma in macaque monkeys with a confocal adaptive optics scanning laser ophthalmoscope (AOSLO). These data will be combined with changes in visual function (standard automated perimetry and electroretinography) and retinal nerve fiber layer (RNFL) thickness (using optical coherence tomography) at corresponding time-points to test the hypothesis that laminar pore changes precede axonal and vision loss in experimental glaucoma. The second aim will determine age-related differences in laminar pore geometry in normal living human eyes using the AOSLO and test the hypothesis that laminar pore size increases with age and is associated with small increases in cupping (measured via fundus photography) and decreased RNFL thickness and visual function. The last aim applies the same methods to measure laminar pore geometry in patients with primary open-angle glaucoma. It will test the hypothesis that larger pore sizes and increased cupping occur in eyes with increasing disease severity and are correlated with decreases in RNFL thickness and visual function. This research plan is based on defining procedures and relationships with experimental glaucoma and extending them to human patients to test their clinical significance. It is aligned with the missions of the NEI and NIBIB in that it investigates a potential mechanism underlying a blinding retinal disease and seeks to improve the diagnosis and assessment of glaucoma in human patients via a new application of a biomedical imaging technique (i.e., AOSLO imaging). The approach is innovative because it uses confocal AOSLO imaging to increase the lateral resolution and contrast of laminar images relative to current clinical instruments, thereby allowing laminar pore geometry to be reliably measured in living normal and glaucomatous eyes. The proposed research is significant because it will lead to more sensitive in vivo imaging techniques to examine structural changes and better clarify the etiology of glaucoma. Ultimately, such knowledge will enhance our understanding of the lamina's role in the development and progression of this disease and may provide an earlier marker of structural damage (i.e., laminar pore alteration) in glaucoma.